Mechanistic Investigation into Rh^III‐Catalyzed Intramolecular Redox‐Neutral Annulation of Aryl Hydrazines with a Tethered Alkyne

Abstract

Am echanistic study of the Cp*Rh III -catalyzed (Cp* = h 5 -pentamethylcyclopentadienyl) intramolecular redox-neutral annulation of tethered alkynes was carried out by density functional calculations using the M06 method. Our results show that the reductive elimination step of the catalytic cycle is rate determining, and the overall energy barrier of the entire process is 31.4 kcal mol À1 (L-II!L-TS8-9). This is in agreement with experimental resultst hat re-portedt he CÀHb ond cleavage not to be the rate-determining step. According to our calculations,t he feasible mechanism for the Rh III !Rh V !Rh III process involves an acylamino migration and subsequent reductive elimination process, which is different from the pathwayp reviously proposed by Li's group.T he present calculations elucidate the experimental observations on the molecular level.[a] W.Scheme1.Rh III -catalyzed intramolecular redox-neutral annulationo fa lkyne-tethered phenylhydrazinea ccording to Li and co-workers. [20] Scheme2.Plausible pathway proposed by Li and co-workers [20] for the Rh III -catalyzed intramolecular redox-neutral annulation of alkyne-tetheredp henylhydrazine.